1. Field of the Invention
This invention relates to direct contact (pebble bed) heat exchangers particularly useful for storage of thermal energy from an intermittent heat source such as the sun.
2. Description of the Prior Art
The discontinuous character of certain forms of energy, such as solar radiation, has long been recognized as one of the challenges to be surmounted in putting such energy to practical use. Storage of energy in thermal form has been recognized as one approach to this challenge which, however, has proved difficult from an efficiency and cost standpoint. Additional challenges have arisen in integrating storage apparatus into a complete energy utilization system such as those producing electrical energy through turbine generator apparatus. Such systems typically require a relatively constant utilization fluid pressure, such as steam pressure at a turbine inlet, which is difficult to obtain from a discontinuous heat source.
In view of the current and projected need for use of discontinuous or significantly varying energy sources, it is therefore desirable to provide efficient and economic thermal storage apparatus and utilization systems incorporating such apparatus.